Human cutaneous and oral cavity papillomas were examined in situ by electron microscopy and fluorescent antibody studies and in vitro by endonuclease restriction enzyme studies and molecular hybridization techniques for evidence of papilloma viruses. Human papilloma virus could be identified in approximately 55% of cutaneous papillomas but in only 5% of oral cavity papillomas. Molecular hybridization studies suggest that there is little if any DNA homology between the most common papilloma virus that causes cutaneous papillomas and those variants that probably cause the oral papillomas.